Miniature loudspeakers are built into numerous mobile devices for reproducing sound, most of which are sold in a highly competitive consumer-electronics market with very tight constraints both in terms of cost, size, and weight, yet demanding a high level of sound quality. Examples for such mobile devices are mobile phones, smart phones, tablets, cameras, and small portable music players.
Components for use in such compact and light-weight mobile devices are therefore subject to severe geometric constraints. Among the geometric constraints are a small foot-print and in particular a small height of the loudspeaker, in order to be suited for mounting in a device with the severe form factor limitations inherent to mobile devices. Typically, the lateral dimensions of a miniature loudspeaker defining its foot-print are between 6 mm and 30 mm, and the axial dimension defining the height of the miniature loudspeaker may be between 1 mm and 5 mm. A typical miniature loudspeaker for mobile applications is therefore a relatively flat, essentially planar device, which typically has a round, rounded, or rectangular contour as seen in the lateral plane.
Mobile devices, such as smartphones and mobile phones, also comprise a multitude of components operating at RF frequencies and emitting electromagnetic radiation in a broad range of frequencies. Due to the compact design of the mobile devices, this results in a high intensity broad band electro-magnetic radiation. When designing components to be used in mobile devices, the susceptibility to a high intensity RF radiation is therefore a further constraint. Owing to the highly compact miniaturized design, planar miniature loudspeakers are typically susceptible to parasitic electromagnetic radiation emitted in the vicinity as electromagnetic interference (EMI), which may be picked up by the voice coil, or other electrical wiring of the miniature loudspeaker, as noise signal affecting the quality of sound reproduction. Further due to the miniaturized design, the miniature loudspeaker is susceptible to harmonic distortion, e.g. due to external load on the mechanical system of the loudspeaker, which again may affect the quality of sound reproduction.
Furthermore, the miniature loudspeaker has to be suited for mounting on a main printed circuit board (PCB) of the mobile device in a high throughput low-cost process. While many electronic devices are suited for surface mounting, miniature loudspeakers are commonly not compatible with such a mounting process, since the heat typically applied during the manufacturing process would affect the permanent magnetic structure included in the speaker. In addition, when mounting the miniature loudspeaker on a main PCB, additional constraints of appropriate vibration-control in the connection between the loudspeaker and the main PCB apply, due to the very nature of the loudspeaker as a sound-pressure/vibration generating device. For example, such miniature loudspeakers are often mechanically clamped to the main PCB using spring-loaded contacts for establishing electrical connections between the loudspeaker and the main PCB. Such spring-loaded contacts may constitute a noticeable item in the total cost of such a miniature loudspeaker, and a lower cost solution is therefore desirable.
It is therefore desirable to provide a miniature loudspeaker suited for consumer market mobile devices overcoming the above mentioned problems. In particular, there is a need for a low-cost miniature loudspeaker module with an improved packaging design suited for reliable low-cost mounting and overcoming the challenges of electromagnetic noise susceptibility and/or harmonic distortion of known packaging designs within the severe constraints on cost and size mentioned above.